1. Field of the Invention
The present invention is directed to the field relating to apparatus and methods used to insert of medical devices in a human or animal body, and in particular apparatus and methods used to insert medical devices into a vascular system or other anatomical cavities.
2. Description of the Prior Art
Development of permanent implantable catheter systems and temporary diagnostic and therapeutic catheters has resulted in life-saving benefits and has greatly improved the quality of life of patients virtually across the entire spectrum of medical treatment. The use of such permanent and temporary catheters in cardiology is a prime, but no means limiting example. In most cases, the catheter must be implanted at the site of application through the use of an introducer. Very often the introducer must be implanted or steered through a tortuous path and positioned at a site some distance from the proximal insertion point. Once the introducer is correctly positioned, an elongate medical instrument is then lead or fed through the introducer, perhaps with the further assistance of guidewires to place it or a selected portion of it at the target site.  With the medical instrument correctly positioned, the introducer is then removed leaving the medical instrument in position.
However, the positioning of the medical instrument can be very delicate. Any force or displacement imparted to the medical instrument by withdrawal of the introducer can potentially dislodge the medical instrument from its intended position, which in turn can be reachieved only with additional procedures of varying difficulty, if at all.
U.S. Pat. No. 4,467,817 to Harris discloses a small diameter pacing lead of carbon filaments surrounded by a stiffening sheath. The tip of the pacing lead extends beyond the stiffening sheath whereby the stiffening sheath is positioned behind the tip of the pacing lead to assist guiding the pacing lead into the desired organ.
U.S. Pat. No. 5,639,276 to Weinstock et. al. describes a cardiac introducer which as a gradient of stiffness along its length so that it is sufficiently soft or flowable at its distal end so that it can pass through the tricuspid valve without causing trauma and is proximally sufficiently stiff so that it can be forced through a tortuous venous path into the apex of the right ventricle of the heart. Nothing is taught in Weinstock or Harris regarding the moldability of the introducer which would allow a reliable lead placement or reliable introducer withdrawal.
A single preshaped guide is frequently inadequate to reach a desired location due to large anatomical variations within the body. What is needed is an apparatus and method for the stable placement of a medical instrument in a body cavity with which apparatus and method there is a decreased risk of  inappropriate lead placement, dislodgment of either the implanted medical instrument by withdrawal of the introducer, dislodgment of the introducer by withdrawal of a shaping tool or other placement device, and the ability to be shaped to conform to the individual's anatomy to reach the desired location.